For this integration you need to capture 3 things from your PayPal account and register a webhook from Bookinglayer inside your PayPal Account.
1. Create an App to get an Account ID and Secret Key.
Go to: PayPal Developers and login with your PayPal account.
Click on: Create App, give it a name (e.g. Bookinglayer). After creation you will have two keys which you need to copy and save in the PayPal Checkout-settings inside your Bookinglayer account: Account ID and Secret Key.
2. Register the webhook and get the Webhook ID
Without this step payments won't be registered in your Backoffice. You can find the Webhook URL in the PayPal Checkout-settings inside your Bookinglayer account. Copy this URL to PayPal and make sure to mark the checkbox for 'Payment capture completed' (leave all other checkboxes unmarked). After creation you will see a Webhook ID, copy this ID and save it under the PayPal Checkout-settings inside your Bookinglayer account.